Opiate receptors [1-5], sites recognizing exogenous opiate drugs and endogenous opiate peptides, include the morphine-preferring .mu. opiate receptor first defined by Martin and colleagues [2]. .mu. receptor distributions and pharmacologic properties place them among the receptors most identified with the analgesic and addicting properties of opiate drugs [3-7]. These receptors are G-linked members of the seven transmembrane domain neuropeptide receptor subfamily [8-14].
Recent studies have identified the cDNAs encoding rodent .mu. [15-17], .delta. [17-19] and .kappa. opiate receptors [20-22], thus defining at least one member of each of the other major opiate receptor subclasses postulated by Martin, Kosterlitz, Hughes, and associates [1-5]. The rat .mu. opiate receptor (.mu. receptor) has the structure of a G-protein coupled receptor. G-protein receptor coupling was confirmed for the rat .mu. receptor [15-17]; morphine affects adenyl cyclase levels in cells expressing .mu. receptor [5,23].
Because of interest in .mu. receptors as targets for development of selective analgesic and anti-addictive therapies [24-28], and because of interest in identifying .mu. receptor gene markers that could detect individuals possessing allelic variants of this gene that could confer differential susceptibility to abused drugs, we have used the rat .mu. opiate receptor cDNA identified in this laboratory [15] to identify its human homolog.